Starting with crappy phone pic
Apple has been doing great on the audio front and though I can fanthom what is up with the Iphone 6 plus, the Iphone 5s seems to be an excellent player as well considering its functions. I still can't live with the Itunes ecosystem and limited format support though. Test were done with Iphone at full volume.
As usual, Apple sticks with minimum phase filters for its device line with only post ringing and no pre ringing unlike linear phase filters.
UPDATE 17.11.2014 with 44.1khz 1 sample width rectangular pulse.
24bit 44.1khz tests of -3dbFS white noise overlayed with a spectrum of a full scale 19.1khz tone to observe the reconstruction filter's behavior. I don't think I can see the aliasing product which is completely suppressed however the harmonic products beyond the 3rd harmonic can be seen. Some stopband rippling of the white noise is also observed. Rising noise floor is partly in fault of the 0404's high frequency limitations.
In THD, the player is well suited for 16 bit audio and little spuraie is observed compared to Sabre based dacs, the consequence? A slightly higher noise floor, I would take this over a Sabre any day.
UPDATE 17.11.2014 with 18 ohm real load -3dbFS THD test, still pretty good.
Same test but at 0dbFS to show clipping performance into 18 ohms.
With the low level resolution test at -90.31dbFS, the Iphone 5 shows fantastic performance and is pretty much spuraie free within the audio band at low levels. Count me impressed. 16 bit quantisation steps were also resolved by the Iphone albeit a little noisily.
24 bit in Blue, 16 bit in red.
In SMPTE IMD, the Iphone 5 beats the ODAC in this test, not much random spikes going on. In CCIF IMD, the difference frequency distortion product at 1khz is rather significant at -90dbFS. Still within the 'range of inaudibility' if you are into that sort of stuff.
Lastly a high resolution FFT spectrum of Dunn Jtest. Noise floor is around the -130dbFS mark which is somewhat worse compared to the EMU0404 but not really much of a concern. No anomalous sidebands are observed. In my books, way better than the DX90's jitter performance.
Jitter spectrum @48khz, 24 bit blue, 16 bit red.
Concluding, its great to see Apple providing decent audio performance for the average consumers. Normal peeps would buy this and get decent performance out of whatever they are listening to. Now if only I could just transfer music without Itunes....
Usual disclaimers: Not science, YMMV.
